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Quartz Heat Transfer
Thanks
to Mike Wheeler of
Arizona
State University for this contribution.
Problem: Quartz heat transfer to connecting joints.
" I have discovered a little trick to keeping the connections cool
so that viton o-rings, greased standard taper joints, etc., won't overheat.
Most of the heat from a furnace tube is transferred to the joints in the
form of light. (Have you ever blown into the open end of a quartz test
tube and
burned your lips? I'm speaking from experience here - it hurts!)
You can eliminate this light pipe transmission of light/heat by adding
two to three marias* between the furnace and
the joint connection. The marias scatter the light and keep the connection
cool. We use this technique for small quartz ampoules and furnace tubes
up to 150mm diameter. This technique has eliminated the previous need for
water cooled metal and glass connectors used in both vertical and horizontal
furnace configurations. This remedy seems almost too easy to be true -
but try it, it really works. |
| We discovered this technique while working on a system that used
a combination of resistance heating and then Rf heating samples to 1600
degC. The open end of the 75mm furnace tube had a custom metal o ring compression
seal that failed most of the time. The light from the furnace traveled
down the quartz tube and was collected by the metal compression fitting
-- destroying the o ring. Using the marias worked very well to control
the heat problem. We have incorporated this into many furnace configurations
since that time with similar results. Vertical furnaces with a connection
at the top of the furnace pose the greatest challenge. At 1000C, the three
marias will keep a Chem Thread, greased ground joint, or flat o ring joint
cool. " |
Mike Wheeler
Arizona State University
* maria - an external ring of glass formed by
heating and pushing the glass tube onto itself.
(see ring seals step
a-c for an illustration)
This information was originally posted in response
to a question placed on the ASGS Technical mail-list.
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